Organic compounds -- part of the class 532-570 series – Organic compounds – Four or more ring nitrogens in the bicyclo ring system
Reexamination Certificate
2000-01-21
2001-05-01
Raymond, Richard L. (Department: 1624)
Organic compounds -- part of the class 532-570 series
Organic compounds
Four or more ring nitrogens in the bicyclo ring system
C544S216000, C428S690000
Reexamination Certificate
active
06225467
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention is generally directed to organic electroluminescent (EL) devices, and more specifically, to organic EL devices with a number of excellent desired performance characteristics, and which devices are desired that are capable of providing uniform luminescence, high electroluminescent efficiency, excellent durability, and low driving voltages. The organic EL devices of the present invention contain an electron transport component comprised of triazine compounds, and which devices can be selected for use in flat-panel emissive display technologies, including TV screens, computer screens, and the like.
PRIOR ART
A simple organic EL device can be comprised of a layer of an organic luminescent material conductively sandwiched between an anode, typically comprised of a transparent conductor, such as indium tin oxide, and a cathode, typically a low work function metal such as magnesium, calcium, aluminum, or the alloys thereof with other metals. The EL device functions on the principle that under an electric field, positive charges (holes) and negative charges (electrons) are respectively injected from the anode and cathode into the luminescent layer and undergo recombination to form excitonic states which subsequently emit light. A number of prior art organic EL devices have been prepared from a laminate of an organic luminescent material and electrodes of opposite polarity, which devices include a single crystal material, such as a single crystal anthracene, as the luminescent substance as described, for example, in U.S. Pat. No. 3,530,325. However, these devices usually require excitation voltages on the order of 100 volts or greater.
An organic EL device with a multilayer structure can be formed as a dual layer structure comprising one organic layer adjacent to the anode supporting hole transport, and another organic layer adjacent to the cathode supporting electron transport and acting as the organic luminescent zone of the device. Another alternate device configuration is comprised of three separate layers, a hole transport layer, a luminescent layer, and an electron transport layer, which layers are laminated in sequence and are sandwiched between an anode and a cathode. Optionally, a fluorescent dopant material can be added to the emission zone or layer whereby the recombination of charges results in the excitation of the fluorescent.
In U.S. Pat. No. 4,539,507 there is disclosed an EL device formed of a conductive glass transparent anode, a hole transporting layer of 1,1-bis(4-p-tolylaminophenyl)cyclohexane, an electron transporting layer of 4,4′-bis(5,7-di-tert-pentyl-2-benzoxzolyl)stilben, and an indium cathode.
U.S. Pat. No. 4,720,432 discloses an organic EL device comprising a dual-layer hole injecting and transporting zone, one layer being comprised of porphyrinic compounds supporting hole injection and the other layer being comprised of aromatic tertiary amine compounds supporting hole transport.
U.S. Pat. No. 4,769,292 discloses an EL device employing a luminescent zone comprised of an organic host material capable of sustaining hole-electron recombination and a fluorescent dye material capable of emitting light in response to energy released by hole-electron recombination. A preferred disclosed host material is an aluminum complex of 8-hydroxyquinoline, namely tris(8-hydroxyquinolinate)aluminum.
Typically, the organic EL devices with multi-layered configurations comprise an electron transport layer in contact with a cathode. This electron transport layer is intended to assist injection of electrons from the cathode into the light-emitting layer. A variety of organic electron transport materials have been employed for this purpose. A class of such electron transport materials is comprised of the metal complexes of 8-hydroxyquinoline, as disclosed in U.S. Pat. No. 4,720,432. A another class of electron transport materials for EL devices is comprised of 1,3,5-oxidiazole compounds, such as those disclosed in
Japanese Journal of Applied Physics
, Part 2, vol. 34, L824 (1995). Also, certain 1,3,5-triazine containing materials have been reported as being a hole blocking layer in organic EL devices, see Fink et al. in
Macromolecular Symposia
, vol. 125, 151 (1997).
While recent progress in organic EL research has elevated the potential of organic EL devices for widespread applications, the performance levels of current available devices may still be below expectations. Further, for visual display applications, organic luminescent materials should provide a satisfactory color in the visible spectrum, normally with emission maxima at about 460, 550 and 630 nanometers for blue, green and red. The aforementioned metal complexes of 8-hydroxyquinoline, such as tris(8-hydroxyquinolinate)aluminum, generally fluoresce in green or longer wavelength region. These electron transport materials may be suitable for use in EL devices with light emission in green or longer wavelength region, however, for blue-emitting EL devices they are of limited use. Although prior art electron transport materials may fluoresce in the blue region, the performance characteristics of the resulting EL devices still possess many disadvantages such as poor operation stability. Thus, there continues to be a need for electron transport materials for organic EL devices, which are suitable for the design of EL devices with satisfactory emission in the visible spectrum of from blue to longer wavelength region. There is also a need for electron transport materials, which can improve EL device operation stability and durability, and a need for electron transport materials, which can enhance the EL charge transporting characteristics, thus lowering device driving voltages. Further, there is a need for electron transport materials for EL device comprised of a cathode comprised of a metal, such as aluminum, and which device can maintain desirable performance characteristics, such as low driving voltage, and excellent operation stability. Further, there is a need for electron transport materials, which are vacuum evaporable and form thin films with excellent thermal stability.
SUMMARY OF THE INVENTION
It is a feature of the present invention to provide improved organic EL devices with many advantages described herein.
It is another feature of the present invention to provide EL devices capable of providing satisfactory emission in the visible spectrum from blue to longer wavelength regions, for example from about 400 nanometers to about 700 nanometers, high electroluminescent efficiency, excellent durability, and low driving voltages, for example from about 10 to about 50 volts, and a luminence value of about 100 cd/m
2
. In another feature of the present invention there are provided organic EL devices comprising an electron transport component comprised of specific triazine compounds, especially those containing biphenyl groups.
Further, in an feature of the present invention there are provided organic EL devices comprised of an anode and a cathode, and an organic luminescent medium containing an electron transport component comprised of triazine compounds, or comprised of a triazine electron acceptor and an amine electron donor connected by a polarizable linkage, such as an aromatic or aryl group.
In another feature of the present invention there are provided organic EL devices comprised of a supporting substrate of, for example, glass, an anode, a buffer layer, a hole transport layer, an electron transport layer, and in contact therewith a metal cathode, wherein the electron transport layer is comprised of an electron transport component comprised of specific novel triazine compounds.
Yet in another feature of the present invention there are provided organic EL devices comprised of a supporting substrate of, for example, glass, an anode, an optional buffer layer, a hole transport layer, a light emitting layer, an electron transport layer, and in contact therewith a metal cathode, wherein the electron transport layer is comprised of an electron transport component compris
Esteghamatian Mohammad
Hor Ah-Mee
Hu Nan-Xing
Ong Beng S.
Popovic Zoran D.
Balasubramanian Venkataraman
Palazzo E. O.
Raymond Richard L.
Xerox Corporation
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